A nock fits into or attaches to the trailing end of an arrow or a crossbow bolt and acts as the means to transfer launching energy between the projectile and the launching device. Lighted nocks, which include a power source as well as a light source powered by the power source, have become increasingly desirable, because they allow tracking the arrow or bolt in flight, as well as locating the arrow or bolt after the shot is taken.
FIG. 1 depicts a crossbow “capture” style nock 10 being received into bore 95 of crossbow bolt 90, as disclosed in application Ser. No. 61/621,211, filed Apr. 6, 2012, and application Ser. No. 13/785,862, filed Mar. 5, 2013, each of which are incorporated herein by reference in their entirety. Nock 10 includes three sections: a proximal end 80, an intermediate portion 60 contiguous with proximal end 80, and distal end 20 that is contiguous with intermediate portion 60. In this embodiment, proximal end 80 is of cylindrical shape and has a diameter that is smaller than the diameters of each of the cylinder-like intermediate portion 60 and distal end 20. Compliant arms 70 project from the surface of intermediate portion 60 and may be arranged in a spiral configuration.
As illustrated in FIG. 1, proximal end 80 and intermediate portion 60 of nock 10 are configured to be received into bore hole 95 of bolt 90. When so received, compression of compliant arms 70 of nock 10 by the inner surface of bore 95 of bolt 90 provides a friction fit that provides one way of attaching nock 10 to bolt 80.
Distal end 20 of nock 10 contains, at its distal end a slot or a groove that provides an opening 40 that is configured to receive the string of a bow or crossbow. Distal end 20 also includes button 50, which may be transparent to allow light produced within nock 10 to be transmitted outside through button 50, and which is configured to turn on the light source of nock 10 when depressed (for example, when depressed due to the tension of the crossbow string during operation). In embodiments in which nock 10 is a lighted nock, nock 10 may also include an internal power source such as a battery to power the internal lighting mechanism. For example, proximal end 80 may be one end of a battery, the other end of which is within intermediate portion 60 (and not depicted in FIG. 1).
Conventional lighted nock systems for both bows and crossbows utilize an optically clear polymeric construction design to transmit light from an LED within the assembly to the outside of the assembly for tracking of the projectile flight, and projectile location after it has stopped flight. Unfortunately, the choices of polymers that are suitable for this application are fairly limited with clear polycarbonate being the most common. The strength of clear polycarbonate is typically limited to a yield strength near 9,000 psi. This has generally been found to not be sufficient, as clear plastic nocks have a history of breakage in normal operation. The breakage of these nocks has become increasingly severe as bows and crossbows have become more powerful. While most nocks have the potential to break upon the projectile striking a target, it has been observed many times that some crossbows will break clear polymeric bodied nocks during the act of firing the projectile. This is very dangerous to the archer and may potentially cause catastrophic damage to the bow or crossbow.
For these reasons, there is a need for a lighted nock adapted for use with arrows or crossbow bolts that is structurally more robust in comparison to previously known lighted nocks.